This invention relates generally to calibration blocks and more particularly, to a universal calibration block for ultrasonic transducers.
Ultrasonic probes are used to inspect many different types of structures. For example, ultrasonic probes may be used to examine piping for wall thickness, weld integrity, and cracking. Ultrasonic probes are used extensively in the nuclear energy industry to examine the various components of a nuclear reactor for stress corrosion cracking. Ultrasonic probes are also used for inspections in the petroleum industry and the aerospace industry, typically for metal cracking, weld integrity, and metal thickness.
To function properly and to provide accurate readings, ultrasonic probes require calibration before use. Usually several different calibrations are performed on an ultrasonic probe utilizing a number of different calibration blocks. For example the following calibrations are typically performed before an ultrasonic probe may be accurately used, determination and verification of beam angle, sweep range calibration, sensitivity calibration including zero degree longitudinal wave sensitivity, shear wave sensitivity, and refracted longitudinal wave sensitivity, ultrasonic flaw detection including horizontal linearity, screen height linearity, and amplitude control linearity, and digital thickness determination. Each calibration generally requires a separate calibration block, or calibration standard. In addition it is often desirous to fabricate the calibration blocks from the same material that the component to be. examined is fabricated from, for example, aluminum, carbon steel, stainless steel, inconel, etc.
A disadvantage to this practice of using different calibration blocks for the various calibrations needed for ultrasonic probes is the need for multiple standard blocks. Another disadvantage is the need to have multiples of each different calibration standard block fabricated from the various materials that are to be examined.
It would be desirable to provide a calibration technique that does not require different calibration blocks for the various calibrations that need to be performed on ultrasonic probes.
These and other objects may be attained by a universal calibration block for calibrating ultrasonic transducer probes. The universal calibration block may be used for all ultrasonic transducer probe calibrations normally performed. The calibration block is typically fabricated from an elongate block of metal. The calibration block includes a first portion located at a first end of the elongate block, a second portion located adjacent the first portion, and a third portion located at a second end of the elongate block and adjacent the second portion.
The first portion includes a first curved section, located at a first end of the elongate block, and a second curved section stepped back from the first curved section. The first curved section has a thickness less than the thickness of the second curved section. The first curved section of the first portion includes a convex curved end surface. The second curved section of the first portion includes a first surface having a convex radius, a second surface adjacent the first surface, having a concave radius, and a substantially straight third surface extending to the second edge of the calibration block. The third part is configured to intersect the second edge of the calibration block at a right angle.
The second portion includes a flat elongate section having a plurality of calibration holes extending therethrough and a plurality of scribe lines located on a first surface of the flat elongate section. The plurality of calibration holes are equally spaced apart from each other in a longitudinal direction and offset from the first edge of the elongate block in equal increasing increments. The first surface of the second portion includes first, second and third scribed lines extending from the calibration hole offset farthest from the first edge of the block to the first edge of the calibration block. The first scribed line extends at an angle of about 45 degrees from a plane intersecting the hole and perpendicular a longitudinal axis of the calibration block. The second line extends at an angle of about 60 degrees from the perpendicular plane, and the third line extends at an angle of about 70 degrees from the perpendicular plane. The first surface of the second portion also includes a fourth scribed line which extends perpendicular from the first edge of the calibration block such that the fourth line intersects the first edge at an apex of the radius of the first surface of the second curved section of the first portion of the calibration block.
The third portion includes a plurality of steps and a plurality of notches. The notches extend from a first edge to a second edge of the calibration block. Typically, the calibration block includes at least three notches. The depth of a first notch is equal to about 80 percent of the thickness of the calibration block measured at the location of the first notch. The depth of a second notch is equal to about 50 percent of the thickness of the block measured at the location of the second notch. The depth of a third notch is equal to about 20 percent of the thickness of the block measured at the location of the third notch. The third portion typically includes at least two steps. A first step having a thickness less than the thickness of the second portion of the elongate block, and a second step having a thickness less than the thickness of the first step. If the calibration block includes additional steps, each succeeding step has a thickness less than the thickness of the preceding adjacent step.
In operation, an ultrasonic transducer probe is placed on the universal calibration block and the following calibration may be performed: flaw depth sizing, linear time base in both depth and metal path, transducer angle verification, transducer index point verification, longitudinal wave resolution and time base verification, and material ultrasonic velocity/delay verification. Each of the above calibrations are performed according to the ultrasonic transducer probe manufacturer""s recommended instructions. However, the above described universal calibration block is substituted for the calibration block recommended by the manufacturer of the ultrasonic transducer probe.
The above described universal calibration block permits the calibration of an ultrasonic transducer probe without requiring different calibration standard blocks for the various calibrations that need to be performed on ultrasonic probes.